The present invention relates to a stage device which is used in an aligner used in a lithography process in manufacture of a semiconductor element or the like, a machine tool used for machining of works and a precision mechanical equipment such as a measuring device or the like for measuring a shape of an object to be measured and moves an object to be positioned such as a work or the like to a target position.
As a device for moving an object to be positioned to a target position, for example, an aligner for use in a lithography process, in which a mask pattern is transferred onto a substrate such as a wafer or the like, in manufacture of a semiconductor element, liquid crystal display element, thin film magnetic head or the like needs to precisely position the wafer, which is an object to be positioned, to a predetermined exposure position. Therefore, the aligner is provided with a wafer stage on which a wafer is mounted and a stage device having a travel mechanism for supplying the wafer stage with thrusts in two directions (X and Y directions) perpendicular to each other.
Thus, the thrusts generated in the travel mechanism must be supplied to the object to be positioned in a highly precise manner without generating a backlash in precision mechanical equipment where an object to be positioned needs to be precisely aligned to a target position. Occurrence of vibration or the like needs to be prevented when the object to be positioned travels.
Therefore, in general, a linear motor, which linearly moves a movable element in no contact with a stator, is used in a conventional travel mechanism constituting a stage device for precision mechanical equipment.
In a constitution disclosed in Japanese Patent Laid-Open Publication No. Hei 11-243132, for example, in a device where thrusts generated by a linear motor are acted on both ends of a stage supported on a base via a static air pressure bearing to move a stage, an inertial body traveling in parallel to the stage is provided on the base. When the stage travels, this inertial body is moved so that a force for canceling a reaction force acting on the base via the linear motor is acted on the base, thereby preventing displacement of the centroid position of the base including the stage and the inertial body. Thus, vibration of the stage is prevented.
In a constitution disclosed in Japanese Patent Laid-Open Publication No. Hei 11-168064, a surface plate is supported on a base via a vibration isolating table or the like. An X-stage provided with a Y-guide bar and a Y-guide bar carrier is provided movably along an X-guide bar on the surface plate. This X-stage is driven in the X direction via an X-axis linear motor and the stators of the X-axis linear motor are supported so that the stators can travel in the X direction on the surface plate via a direct acting guide. Thus, a damping force for canceling a reaction force when the X-stage is driven is given to the stators by an X-damping member attached to a damping frame fixed on the base.
A bottom surface and an outer surface of a first Y-guide bar carrier are provided with air exhaust nozzles each constituting a bearing. Furthermore, a pre-load mechanism such as a magnet, vacuum pocket or the like is installed in the vicinity of these air exhaust nozzles. The first Y-guide bar carrier can travel in the X direction maintaining a certain gap with a surface of the surface plate and a side surface of an X-guide bar while being confined in the Z direction and Y direction. Similarly, an air exhaust nozzle constituting an air bearing and a pre-load mechanism such as a magnet, vacuum pocket or the like are also installed in a bottom surface of a second Y-guide bar carrier. Thus, the Y-guide bar carrier can also travel in the X direction maintaining a certain gap with the top surface of the surface plate while being confined.
With this constitution, when the movable section travels, occurrence of a moment, deforming force and the like is prevented and thereby vibration can be prevented.
In a constitution disclosed in Japanese Patent Laid-Open Publication No. Hei 8-63231, a movable stage device uses a rectifying linear motor. The linear motor moves a guideless stage in one linear motion direction and allows the stage to perform a fine yaw rotation in a plane. A carrier/jogging element holding a single voice coil motor is controlled so as to generally follow the stage traveling in the linear motion direction. A voice coil motor is given an electromagnetic force in a plane so that the stage is allowed to perform a fine motion in a direction perpendicular to the linear motion direction to achieve an appropriate alignment. Furthermore, one element (coil or magnet) of the rectifying linear motor is provided on a driving frame which can travel freely on the plane. The driving frame is driven by a reaction force so that the centroid position of the device is maintained. In this constitution, when one linear motor is used, two voice coil motors are used to correct the yaw rotation.
In a conventional stage device, however, when an object to be positioned is moved in one of two directions perpendicular to each other and then moved in the other remaining direction, the object to be positioned may not be positioned in the driving center of a drive mechanism (central position between the linear motors when the drive mechanism is constituted by a pair of linear motors in parallel in the other remaining direction). Also, the centroid position of the object to be positioned in a direction perpendicular to two respective traveling directions may not be positioned in the driving center of the drive mechanism depending on the shape of the object to be positioned. When the object to be positioned travels in this state, the object to be positioned is deflected in a yawing or pitching direction and thereby the object to be positioned cannot be moved precisely to a target position.
Accordingly, an object of the present invention is to provide a stage device which can prevent deflection of an object to be positioned and a stage in a yawing or pitching direction due to displacement of the centroid position thereof when the object to be positioned travels and move the object to be positioned precisely to a target position and to provide a stage device which can prevent vibration of a support due to movement of the stage and move the object to be positioned precisely to a target position.
The present invention is provided with the following constitutions to achieve the above object.
(1) A stage device which moves a stage on a support by thrusts generated by a pair of thrust generating means in parallel to a stage traveling direction is characterized in that there is provided a control section for moving a stage in a state that moments acted on the stage around the centroid are balanced by the thrusts supplied from each of the pair of thrust generating means.
In this constitution, when the stage travels, the moments about the centroid of the stage are balanced. Therefore, the stage traveling direction is not deflected in a yawing direction and thereby the object to be positioned can be precisely moved to a target position.
(2) The stage device is characterized in that the control section relatively changes the thrust generated by each of the pair of thrust generating means depending on the centroid position of the stage in a direction perpendicular to its traveling direction.
In this constitution, the respective thrusts of the pair of thrust generating means are determined so that the moments about the centroid of the stage are balanced depending on the centroid position of the stage in a direction perpendicular to its traveling direction when the stage travels. Therefore, irrespective of the centroid position of the stage in a direction perpendicular to its traveling direction, the moments acted on the stage about its centroid are balanced by the respective thrusts from the pair of thrust generating means and thereby the stage traveling direction is not deflected to a yawing direction.
(3) The stage device is characterized in that the control section allows the centroid position of the stage to coincide with a central position in a direction perpendicular to the traveling direction before moving the stage.
In this constitution, the stage travels in a state that the centroid position of the stage is positioned at the center in a direction perpendicular to the traveling direction. Therefore, moments acted on the stage about its centroid are balanced by the respective thrusts from the pair of thrust generating means at all times by keeping the respective thrusts from the pair of thrust generating means equal to each other. Thus, the stage traveling direction is not deflected in a yawing direction.
(4) The stage device is characterized in that the control section calculates a thrust Fa to be generated by the thrust generating means on a distance La side and a thrust Fb to be generated by the thrust generating means on a distance Lb side by the following equations:
Fa=Fxc3x97Lb/(La+Lb) 
Fb=Fxc3x97La/(La+Lb) 
where F is a thrust required to move the stage and La and Lb are distances from the centroid position of the stage to positions where the respective thrusts of the pair of thrust generating means act, respectively.
In this constitution, the thrusts Fa and Fb of the respective thrust generating means required to move the stage are calculated based on the distances La and Lb from the centroid position of the stage to positions where the respective thrusts of the pair of thrust generating means act. Therefore, thrusts required to move the stage are distributed to the pair of thrust generating means in a state that moments about the centroid obtained as a product of thrusts of the respective thrust generating means and a distance from the centroid position to action points of the thrusts in the stage are balanced.
(5) The stage device is characterized in that an object to be positioned is placed on the stage movably in one of two directions perpendicular to each other while the stage travels in the other direction. There is provided a position detecting sensor for detecting a position of the object to be positioned in the stage. The control section calculates a value of current to be supplied to each of the pair of thrust generating means for supplying thrusts in the other direction to the stage based on a detection result of the position detecting sensor.
In this constitution, the value of current for the pair of thrust generating means for supplying thrusts to the stage is calculated based on the detection result in the position of the object to be positioned in the direction perpendicular to the stage traveling direction. Therefore, a thrust depending on the value of current calculated based on the centroid position of the stage determined by the position of the object to be positioned is supplied to the stage from each of the pair of thrust generating means. Thus, the stage travels in a state that the moments about the centroid are balanced.
(6) The stage device is characterized in that the centroid position of the object to be positioned, the centroid position of the stage, the action point of the moving force against the object to be positioned and the action point of the thrust against the stage exist in the same plane having a normal line perpendicular to the traveling direction of the object to be positioned and the stage traveling direction.
In this constitution, the centroid position and the action point of the moving force of the object to be positioned and the centroid position and the action point of the thrust of the stage are positioned in the same plane having a normal line perpendicular to the traveling direction of the object to be positioned and the stage traveling direction. Therefore, the moving force supplied to the object to be positioned and the thrust supplied to the stage do not generate a moment in a pitching direction in the object to be positioned.
(7) The stage device is characterized in that the pair of thrust generating means for supplying thrusts to the stage contains a movable element fixed to the stage and stators attached to a support movably in the stage traveling direction.
In this constitution, the stators of the thrust generating means for supplying thrusts to the stage are attached to the support movably in the stage traveling direction. Therefore, when the stage travels, reaction forces acted on the stators of the thrust generating means do not act on the support and thereby no vibration is generated in the support.
(8) A stage device for linearly moving a stage via a guide fixed on a base is characterized in that there are provided a first thrust generating means for supplying a thrust depending on the centroid position of the stage to each of both end portions thereof in a direction perpendicular to the stage traveling direction and a second thrust generating means for acting a force on the base opposite to a reaction force transmitted from the first thrust generating means to the base when the stage travels.
In this constitution, a thrust depending on the centroid position of the stage is supplied to both ends of the stage and a force opposite to a reaction force transmitted to the base acts on the base when the stage travels. Therefore, when the stage travels, a force in a yawing direction does not act on the stage by supplying each of the both ends of the stage with a thrust inversely proportional to the distance to the centroid position of the stage. Also, a reaction force transmitted to the base in the yawing direction is canceled by the movement of the stage and thereby the base does not cause yawing.
(9) The stage device is characterized in that the first thrust generating means determines or distributes a thrust Fa to be supplied to the end portion on the distance La side and a thrust Fb to be supplied to the end portion on the distance Lb side by the following equations:
Fa=Fxc3x97Lb/(La+Lb) 
Fb=Fxc3x97La/(La+Lb) 
where F is a thrust required to move the stage and La and Lb are distances from the centroid position of the stage to action points of the thrusts in both end portions of the stage.
In this constitution, a thrust inversely proportional to the distance to the centroid position of the stage is supplied to each of the both ends of the stage. Therefore, the stage does not yaw when the stage travels.
(10) The stage device is characterized in that the second thrust generating means is an inertial body which freely moves in a plane in parallel to a plane on which the stage travels in the base and receives a thrust supplied from the base.
In this constitution, the inertial body travels in a plane in parallel to the plane on which the stage travels depending on a reaction force acting on the base when the stage travels. Therefore, when the stage travels, the inertial body travels relatively to the base and a force opposite to the reaction force by the movement of the stage acts from the inertial body on the base. Thus, the base does not rotate in a yawing direction.
(11) The stage device is characterized in that the second thrust generating means travels without contacting the base in a plane in parallel to the plane on which the stage travels.
In this constitution, the centroid position of the base is not moved in a plane in parallel to the plane on which the stage travels by acting a force opposite to the reaction force when the stage travels on the base. When yawing of the base is controlled by acting a force opposite to the reaction force, it is not necessary to consider movement of the centroid position of the base by acting a force opposite to the reaction force.
(12) The stage device is characterized in that the second thrust generating means are disposed at two sites of the base and receive a supply of thrusts Fc, Fd determined or distributed by the following equations:
Fc=xe2x88x92Fx{(Ld+Le)/(Lc+Ld)}
Fd=xe2x88x92Fx{(Lcxe2x88x92Le)/(Lc+Ld)}
where Fx is a thrust required to move the stage, Le is a distance from the centroid position of the stage to the centroid position of the base and Lc and Ld are distances from the thrust generating positions in the second thrust generating means to the centroid position of the base.
In this constitution, moments about the centroid acting on the base by the movement of the stage are canceled by the movement of the inertial body. Therefore, when the stage travels, the moments about the centroid of the base are balanced and thereby the base does not rotate in a yawing direction by the moments about the centroid of the base.
(13) The stage device is characterized in that the stage is composed of an X-direction stage and Y-direction stage traveling in directions perpendicular to each other. The first thrust generating means is composed of a first X-direction thrust generating means and a first Y-direction thrust generating means for generating a thrust to be supplied to each of the X-direction stage and the Y-direction stage. The second thrust generating means is composed of a second X-direction thrust generating means and a second Y-direction thrust generating means for acting a force opposite to reaction forces transmitted to the base from the first X-direction thrust generating means and the first Y-direction thrust generating means on the base. There are provided first to fourth supports holding the base at four sites in a plane in parallel to the plane on which the X-direction stage and the Y-direction stage travel.
Bearing powers Fxcex1, Fxcex2, Fxcex3, Fxcex4 of the first to fourth supports are determined and distributed by the following equations:
Fxcex1={Lxcex2/(Lxcex1+Lxcex2)}{Lxcex4/(Lxcex3+Lxcex4)}W 
Fxcex2={Lxcex1/(Lxcex1+Lxcex2)}{Lxcex4/(Lxcex3+Lxcex4)}W 
Fxcex3={Lxcex1/(Lxcex1+Lxcex2)}{Lxcex3/(Lxcex3+Lxcex4)}W 
Fxcex4={Lxcex2/(Lxcex1+Lxcex2)}{Lxcex3/(Lxcex3+Lxcex4)}W 
where W is a weight of the base including the X-direction stage and Y-direction stage, Lxcex3 and Lxcex4 are distances from the centroid position of the base to the two positions where the supports are disposed in the traveling direction of the X-direction stage and Lxcex1 and Lxcex4 are distances from the centroid position of the base to the two positions where the supports are disposed in the traveling direction of the Y-direction stage.
In this constitution, the respective bearing powers of the four supports for supporting the base are determined or distributed based on the distance from each support to the centroid position of the base. Therefore, the moments about the centroid of the base generated by the movement of the stage in a plane perpendicular to the plane on which the stage travels are canceled by the bearing powers of the supports depending on the centroid position of the base when the stage travels. Thus, the base does not rotate in a pitching direction.